(Adds comment on call between S.Korean and U.S. defense chiefs)
* World escapes threat of war, nuclear weapons after summit - Moon
* Pompeo says took "very good, significant step" in Singapore
* China's Xi urges unremitting efforts for political resolution
* Japan PM seeking summit with N.Korea's Kim in Pyongyang - report
By Christine Kim and Michael Martina
SEOUL/BEIJING, June 14 (Reuters) - Tough sanctions will remain on North Korea until its complete denuclearisation, the U.S. secretary of state said on Thursday, apparently contradicting the North's view that the process agreed at this week's summit would be phased and reciprocal.
U.S. President Donald Trump and North Korean leader Kim Jong Un issued a joint statement after their meeting in Singapore this week that reaffirmed the North's commitment to "work toward complete denuclearisation of the Korean peninsula", while Trump "committed to provide security guarantees".
Trump later told a news conference he would end joint U.S.-South Korean military exercises.
"President Trump has been incredibly clear about the sequencing of denuclearisation and relief from the sanctions," Secretary of State Mike Pompeo told reporters after meeting South Korea's president and Japan's foreign minister in Seoul.
"We are going to get complete denuclearisation; only then will there be relief from the sanctions," he said.
North Korean state media reported on Wednesday that Kim and Trump had recognised the principle of "step-by-step and simultaneous action" to achieve peace and denuclearisation on the Korean peninsula.
The summit statement provided no details on when North Korea would give up its nuclear weapons programme or how the dismantling might be verified.
Sceptics of how much the meeting achieved pointed to the North Korean leadership's long-held view that nuclear weapons are a bulwark against what it fears are U.S. plans to overthrow it and unite the Korean peninsula.
However, South Korean President Moon Jae-in said the world, through the summit, had escaped the threat of war, echoing Trump's upbeat assessment of his meeting with Kim.
"What's most important was that the people of the world, including those in the United States, Japan and Koreans, have all been able to escape the threat of war, nuclear weapons and missiles," Moon told Pompeo.
Pompeo insisted North Korea was committed to giving up its nuclear arsenal but said it would "be a process, not an easy one".
Kim understood getting rid of his nuclear arsenal needed to be done quickly and there would only be relief from stringent U.N. sanctions on North Korea after its "complete denuclearisation", Pompeo said.
Moon later said South Korea would be flexible when it comes to military pressure on North Korea if it is sincere about denuclearisation.
Also on Thursday, North and South Korea held their first military talks in more than a decade. The talks followed on from an inter-Korean summit in April at which Moon and Kim agreed to defuse tension and cease "hostile acts".
Speaking later in the day in Beijing, Pompeo said China, Japan and South Korea all acknowledged a corner had been turned on the Korean peninsula issue, but that all three had also acknowledged sanctions remain in place until denuclearisation is complete.
"China has reaffirmed its commitment to honouring the U.N. Security Council resolutions. Those have mechanisms for relief contained in them, and we agreed that at the appropriate time that those would be considered," Pompeo said, standing next to the Chinese government's top diplomat, State Councillor Wang Yi.
"But we have made very clear that the sanctions and the economic relief that North Korea will receive will only happen after the full denuclearisation, the complete denuclearisation of North Korea."
Wang said China had consistently supported the denuclearisation of the Korean peninsula but that it was impossible to solve the issue overnight.
"At the same time, we believe North Korea's reasonable security concerns should be resolved."
Chinese President Xi Jinping told Pompeo that he hoped the United States and North Korea could keep making unremitting efforts for a political resolution, and that China was willing to keep playing a constructive role in this process, a foreign ministry statement said.
'EVERYBODY MUCH SAFER'
The United States has long insisted on complete, verifiable and irreversible denuclearisation by North Korea.
But the summit statement reference to North Korea committing to work towards the complete denuclearisation of the peninsula has used been by North Korea in the past to include a U.S. nuclear umbrella in the region, and echoes promises it has failed to keep.
"They made real commitments to denuclearise. Each of them. And President Trump made a commitment that he would provide security assurances that were commensurate with that," Pompeo said in Beijing.
"Those are firm commitments that the two leaders made and an understanding of the programme is a piece of what will ultimately lead to our capacity to verify that full and complete denuclearisation has actually taken place."
Trump returned to the United States on Wednesday and took to Twitter to hail the meeting, the first between a sitting U.S. president and a North Korean leader, as a major win for American security.
"Everybody can now feel much safer than the day I took office," Trump tweeted. "There is no longer a nuclear threat from North Korea."
Democratic critics in the United States said the agreement was short on detail and the Republican president had made too many concessions to Kim, whose country is under U.N. sanctions for its nuclear and weapons programmes and is widely condemned for human rights abuses.
Pompeo said Trump's comments about the reduced threat from North Korea were made "with eyes wide open".
"It could be the case that our effort won't ... work but we are determined to set the conditions so that we can right this failure of decades and reset the conditions for North Korea's participation in the community of nations," Pompeo said after a trilateral meeting with South Korean Foreign Minister Kang Kyung-wha and Japanese Foreign Minister Taro Kono.
Japan has reacted to Trump's plan to cancel military exercises with South Korea with concern, saying the drills are vital for East Asian security.
Two North Korean missiles flew over Japan last year as North Korea made rapid advances in developing a missile capable of striking the U.S. mainland with a nuclear warhead.
Tokyo is working on arranging a meeting between Prime Minister Shinzo Abe and Kim, with one possibility being an Abe visit to Pyongyang around August, the Yomiuri newspaper reported.
A Japanese government source familiar with the matter told Reuters officials aimed to discuss a summit with North Korean officials at a regional security conference in Mongolia on Thursday and Friday.
Kang said South Korea and the United States shared the same goals and approach to achieving denuclearisation.
"The issue of South Korea-U.S. joint exercises is one that should be discussed," Kang said. "But the issues of the alliance should be dealt with under the premise we maintain a joint ironclad defence posture."
The U.S. intelligence assessment of the nuclear and other military threat posed by North Korea to U.S. and allied forces remained unchanged despite Trump's and Moon's assertions about the North Korean nuclear threat being over, a senior U.S. official responsible for studying the North Korean military said.
U.S. officials said it was unclear what types of training involving U.S. and South Korean troops might cross into Trump's now forbidden zone of "war games". But big, joint U.S.-South Korean exercises appeared off-limits under the new guidance.
"Make no mistake, we are going to maintain the readiness of our forces in South Korea," said one U.S. official, speaking on condition of anonymity. The official acknowledged, however, it was still not certain how that was going to happen.
The Pentagon said U.S. Defense Secretary Jim Mattis spoke with his South Korean counterpart on Thursday and in a phone call discussed how they would work together to meet Trump's guidance on joint military exercises.
Mattis also spoke with his Japanese counterpart, Itsunori Onodera, and a Pentagon statement after the call said: "The United States reaffirmed its ironclad defense commitments to Japan and its determination to maintain the readiness of its forces in the region."
The United States maintains about 28,500 soldiers in South Korea, which remains in a technical state of war with the North after the 1950-53 Korean War ended in a truce rather than a peace treaty.
(Reporting by David Brunnstrom and Christine Kim in SEOUL Additional by Josh Smith and Hyonhee Shin in SEOUL, Yoshifumi Takemoto and Chang-Ran Kim in TOKYO, Ben Blanchard in BEIJING and Phil Stewart in WASHINGTON Editing by Robert Birsel and James Dalgleish)
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